1. Field of the Invention
The present invention relates to an optoelectronic packaging substrate provided with optical wiring having an optical waveguide and electric wiring and useful in electric, electronic, and communication fields and its production method.
2. Related Art
Polysilanes are polymers very attractive in terms of metallic property and non-localization of electrons of silicon as compared with carbon, as well as high heat resistance and excellent thin film formability and utilization of such polysilanes leads to production of highly conductive materials by a method for doping iodine, a method for doping ferric chloride, and the like. Further, for the purpose to develop photoresist for forming various fine patterns with high precision, investigations into the use of the polysilanes have been actively preformed and many proposal have been disclosed in, for example, Japanese Patent Publication Laid Open Nos. H6-291273 and H7-114188.
Further, in Japanese Patent Publication Laid Open No. H5-72694 is disclosed a method for fabricating semiconductor integrated circuits by using a polysilane. This method is characterized in that a polysilane or a polysilane film doped with iodine or the like is used as a conductive layer and a siloxane film converted from the polysilane by light radiation is used as an insulating layer and in such a manner, it has been tried to use a polymer having Si—Si bonds for a conductive material.
However, with respect to a semiconductor integrated circuit obtained by the foregoing method, sufficient conductivity of a conductive part cannot be provided only by a polysilane and also, use of corrosive iodine or the like causes significant inverse effects in the case of applications to electronic materials and attributed to the utilization of the polysilane itself, which is easily converted into siloxane by water in atmospheric air, oxygen, light and the like, as a conductive material, it has been extremely difficult to use the polysilane for electronic materials especially required to have reliability.
Further, Japanese Patent Publication Laid Open No. S57-11339 discloses a method for forming a metal image by exposing a compound having Si—Si bonds and then bringing the compound into contact with a metal salt solution. Based on the reduction of the metal salt to a metal by contact of the compound having Si—Si bonds with the metal salt solution, the method forms a metal layer in the unexposed part.
Also, according to Japanese Patent Publication Laid Open No. H10-326957 disclosed is a method for forming metal patterns by radiating light to a film of a solely polysilane, doping the exposed parts with a palladium salt, which is a catalyst for electroless plating, and carrying out electroless plating using the catalyst in the exposed parts. However, a polysilane film, in general, has high crystallinity and becomes a hard and fragile film, so that even if such metal patterns are formed, the metal patterns are inferior in adhesion strength and thus no practically usable metal pattern can be formed. Moreover, since the plated portions are grown on the surface of the polysilane film, they become uneven and in the case of application to multilayered built-up substrate, multi-chip module substrate, and the like, surface smoothing treatment is required to result in setback for practical use.
Meanwhile, based on the fact that bond scission of polysilane occurs easily by UV radiation, electron beam radiation, or the like and consequently the refractive index is decreased, application of a polysilane to an optical waveguide is disclosed in Japanese Patent Publication Laid Open No. H6-22234. The process of forming the waveguide only by light radiation can shorten the process time and make the production easy, however the linear polysilane described there is extremely physically fragile owing to the high crystallinity and in the case of use it for an optical waveguide, the loss is high owing to light dispersion. Moreover, it is difficult in terms of physical property and surface smoothness to form electric wiring by plating in the foregoing manner simultaneously with the optical waveguide.
Similarly, investigations into practical application of polymer materials for photoelectric compound mounting substrates have been made by using polyimide type materials. The investigations include methods for producing optoelectronic packaging substrates by forming a fluorinated polyimide, which has been found actual usable for optical waveguides, on semiconductor substrate and then separating an optical waveguide portion, and laminating it on an electric circuit substrate. The optical waveguide of the fluorinated polyimide requires an etching step in vacuum and the size or the like of the substrate is therefore limited to make the method not practical. Further, since the electric wiring is to be formed by a conventional etching method using a copper foil, there is limit in terms of mounting with a high density and as a result, the method has many problems as a technique to deal with high frequency for the photoelectric wiring compound mounting.
A technology for simultaneously forming an optical waveguide, electric wiring, and electronic parts such as a capacitor and the like in a single substrate requires a material for the optical waveguide and a material for electric wiring to similarly satisfy properties such as high transparency, low light loss, high electric insulation, and low dielectric constant and any conventional techniques and materials have not been satisfactory.